MISTER CAINBRIDGE WAS a West Indian merchant who owned a small grocery store in Harlem. From early morning to late evening he sat in front of his store next to the vegetables, on a wooden milk crate with a faded pillow on top that served as a cushion. There, six days a week, beneath the heavy brown canvas awning, cranked down over the store window, he sat, representing an approachable throne of earthly grace, where a familiar face was trusted to buy food on credit, and during these depressive days of 1938, everybody needed a little extra time to pay for food.